<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>s04-计算属性和侦听器</title>
		<!-- <script src="../vue.js"></script> -->
		<script src="https://cdn.jsdelivr.net/npm/vue@2.7.7/dist/vue.js"></script>
		<!-- 因为 AJAX 库和通用工具的生态已经相当丰富，Vue 核心代码没有重复 -->
		<!-- 提供这些功能以保持精简。这也可以让你自由选择自己更熟悉的工具。 -->
		<script src="https://cdn.jsdelivr.net/npm/axios@0.12.0/dist/axios.min.js"></script>
		<script src="https://cdn.jsdelivr.net/npm/lodash@4.13.1/lodash.min.js"></script>

	</head>
	<body>
		<div id="app1">
			<p>original message: {{message}}</p>
			<p>reversed message: {{reversedMessage}}</p>
			<p>reversed message2: {{reversedMessage2()}}</p>
		</div>
		<hr />
		<div id="app2">
			firstName: {{firstName}}<br />
			lastName: {{lastName}}<br />
			fullName: {{fullName}}
		</div>
		<hr />
		<div id="app3">
			firstName: {{firstName}}<br />
			lastName: {{lastName}}<br />
			fullName: {{fullName}}
		</div>
		<hr />
		<div id="app4">
			firstName: {{firstName}}<br />
			lastName: {{lastName}}<br />
			fullName: {{fullName}}
		</div>
		<hr />
		<div id="app5">
			<p>
				ask a yes/no question: 
				<input v-model="question" />
			</p>
			<p>{{answer}}</p>
		</div>
		<hr />
		<script type="text/javascript">
			var vm = new Vue({
				el: '#app1',
				data: {
					message: 'hello'
				},
				// 计算属性
				computed: {
					// 计算属性的 getter
					// reversedMessage: function() { // 原始写法
          reversedMessage() { // 简洁写法：此处省略了 ": function()"
						// `this` 指向 vm 实例
						return this.message.split('').reverse().join('')
					}
				},
				// 方法
				methods: {
					reversedMessage2: function() {
						return this.message.split('').reverse().join('')
					}
				}
			})
			console.log(vm.message, "vm.message")
			console.log(vm.reversedMessage, "vm.reversedMessage")
			vm.message = 'world'
			console.log(vm.message, "first vm.message")
			console.log(vm.reversedMessage, "second vm.reversedMessage")
			
			// 侦听属性 watch
			var vm2 = new Vue({
				el: '#app2',
				data: {
					firstName: 'Foo',
					lastName: 'Bar',
					fullName: 'Foo Bar'
				},
				watch: {
					firstName: function(val) {
						this.fullName = val + ' ' + this.lastName
					},
					lastName: function(val) {
						this.fullName = this.firstName + ' ' + val
					}
				}
			})
			vm2.firstName = 'witt'
			vm2.lastName = 'zhang'
			
			// 侦听属性 改为 计算属性，代码简洁优雅多了
			var vm3 = new Vue({
			  el: '#app3',
			  data: {
			    firstName: 'Foo',
			    lastName: 'Bar'
			  },
			  computed: {
			    fullName: function () {
			      return this.firstName + ' ' + this.lastName
			    }
			  }
			})
			vm3.firstName = 'witt'
			vm3.lastName = 'zhang'
			
			// 计算属性的 setter
			var vm4 = new Vue({
			  el: '#app4',
			  data: {
			    firstName: 'Foo',
			    lastName: 'Bar'
			  },
			  computed: {
			    fullName: {
					// getter
					get: function () {
					  return this.firstName + ' ' + this.lastName
					},
					set: function(newValue) {
						var names = newValue.split(' ')
						this.firstName = names[0]
						this.lastName = names[1]
					},
				}
			  }
			})
			
			// 侦听器：当需要在数据变化时执行异步或开销较大的操作时，这个方式是最有用的
			var vm5 = new Vue({
				el: '#app5',
				data: {
					question: '',
					answer: 'I cannot give you an answer until you ask a question!'
				},
				watch: {
					// 如果 `question` 发生改变，这个函数就会运行
					question: function(newQuestion, oldQuestion) {
						this.answer = 'Waiting for you to stop typing...'
						this.debouncedGetAnswer()
					}
				},
				created: function() {
					// `_.debounce` 是一个通过 Lodash 限制操作频率的函数。
					// 在这个例子中，我们希望限制访问 yesno.wtf/api 的频率
					// AJAX 请求直到用户输入完毕才会发出。想要了解更多关于
					// `_.debounce` 函数 (及其近亲 `_.throttle`) 的知识，
					// 请参考：https://lodash.com/docs#debounce
					this.debouncedGetAnswer = _.debounce(this.getAnswer, 500)
				},
				methods: {
					getAnswer: function() {
						if (this.question.indexOf('?') === -1) {
							this.answer = 'Questions usually contain a question mark. ;-)'
							return
						}
						this.answer = 'thinking...'
						var vvmm = this
						axios.get('https://yesno.wtf/api')
							.then(function (response) {
								vvmm.answer = _.capitalize(response.data.answer)
							})
							.catch(function (error) {
								vvmm.answer = 'Error! Could not reach the API. ' + error
							})
					}
				}
			})
		</script>
	</body>
</html>
